The invention relates generally to nondestructive methods for determining the integrity of components and structures. More particularly, the invention is a method and circuit used in a system for nondestructive test method qualification and probability of detection determination, for establishing and maintaining nondestructive testing proficiency of inspectors, for periodically presenting flaw signals to inspectors during routine inspections, and for ensuring sufficient scan coverage for detection of material defects in a test piece. The invention enables the injection of a virtual flaw signal into an NDT system that makes use of eddy current testing (ECT) to detect the presence of flaws in components and structures.
Nondestructive testing (NOT) is used in many industries to detect the presence of flaws so that the integrity of components and structures may be determined. NDT involves using various test methods, such as eddy current and ultrasonics. Applications include military and civilian aircraft, fossil and nuclear electrical power generation equipment, petrochemical plants, etc. There are several needs within the NDT environment that, if satisfied, would significantly reduce inspection costs and improve the reliability and quality of inspections.
NDT method qualification and probability of detection (POD) determination is one area of need. Demonstration of the capability and reliability of new NDT techniques must often be done in a short period of time and at minimal cost. The present approach is to perform a POD study. These studies involve producing many test specimens with realistic flaws, training multiple NDT technicians, and conducting blind tests. Fabrication of the flawed specimens is very expensive and time consuming. As a result, a POD study is usually performed only for the most critical applications. A system and method to reduce costs and time required to implement POD studies is needed.
NDT inspectors must be trained to ensure proficiency in new and existing NDT procedures. Training is also required periodically in order to maintain proficiency of the inspectors. Although specimens with realistic flaws are needed for training, they are often not available. Video-based training courses are available, but they do not provide xe2x80x9chands-onxe2x80x9d experience with real flaws. Therefore, better training methods are another area of need.
Monitoring existing inspections when flaws are infrequent presents another area of need. In some routine inspections, flaws are encountered very infrequently, sometimes less than once per year. Inspectors may become conditioned to not expecting flaws, resulting in a loss of proficiency. A method is needed to periodically present simulated flaws to inspectors during routine inspections.
Ensuring that a thorough scan is conducted over an entire test piece in another area of need. Some inspections are performed by hand scanning, and the scanning coverage of the appropriate area is dependent on the skill and attention of the operator. A method is needed to monitor scan position so that proper coverage is obtained.
The purpose of the present invention is to enable virtual flaw signal injection into a NDT system that relies on eddy current testing (ECT) to inspect a test piece. This enables reliability testing and training to be performed without the need for actual flaws. The method and circuit disclosed herein is used with a simulator to inject virtual flaw signals into a probe input terminal of ECT instrumentation. The signal injection is performed without interfering with normal ECT instrument probe operation or with signals from the probe. The invention is able to inject virtual flaw signals while allowing the ECT instrumentation to be responsive to existing flaws and geometry features of a work piece, as well as variations in the probe""s distance from or orientation to the work piece.
The present invention provides for a method and circuit that enables ECT instrumentation to satisfy the needs for reducing costs and time required to implement POD studies, providing improved realistic training methods, presenting simulated flaws to inspectors during routine inspections, and for monitoring scan position to ensure proper coverage of test pieces. This invention enables a simulation system to perform the functions of an NDT inspection simulator analogous to flight simulators used to train aircraft pilots. The operations of the NDT simulator using the present invention are transparent to the inspector using the system when realistic, virtual flaw signals are presented at preprogrammed locations on the actual test piece. The virtual flaw signals may be premeasured or generated from a model. This method of presenting virtual flaws provides the equivalent of real flaws to an inspector without the requirement for having actual flaws in a test piece. The inspector may use the same probes and instrumentation of a conventional ECT instrument that are normally used in the inspection process. The injection circuit comprising the present invention may be connected between the probe and ECT instrument so that flaw responses will be injected into the instrument, and the operator may view a response on the actual ECT instrument display. The probe and instrument may remain xe2x80x9clivexe2x80x9d, so that the interaction between the probe and the test piece remain active as well. The simulator may track the probe position so that responses from flaws can be injected at a selected location on the test piece.
The present invention enables POD tests to be accomplished without the need for manufacturing a large number of actually flawed test pieces. A training mode may be implemented in which the inspector receives instructions from the system and can practice with the equivalent of actual flawed test pieces. The system may be used with routine inspections to inject virtual flaw signals to keep inspectors alert, and may be used to monitor probe position in manual test scans to ensure proper coverage.
An embodiment of the present invention is a method for injecting virtual flaw signals into a nondestructive test system, comprising the steps for moving a test probe over a test piece by an inspector, providing an excitation signal from the nondestructive test system to the test probe and a virtual flaw injection circuit, determining virtual flaw parameter signals from test probe position signals and a stored virtual flaw map for the test piece, sending the virtual flaw parameter signals and an output signal from the test probe to the virtual flaw injection circuit, processing the excitation signal and the test probe output signal using the virtual flaw parameter signals for generating a virtual flaw response signal by the virtual flaw injection circuit, transmitting the virtual flaw response signal to a test probe input of the nondestructive test system, and displaying actual and virtual flaws to the inspector from the nondestructive test system. The step for determining virtual flaw parameter signals may further comprise the steps for reading test probe position signals for indicating test probe positions relative to a test piece, reading test probe liftoff measurement signals for indicating test probe liftoff from the test piece, reading a virtual flaw map for the test piece stored in a memory for determining uncorrected virtual flaw parameter signals based on the test probe position signals, and applying a liftoff correction based on the lest probe liftoff measurement signals to the uncorrected virtual flaw parameter signals for determining corrected virtual flaw parameter signals. The step for processing may further comprise the steps for modulating an amplitude of the excitation signal by the virtual flaw parameter signals, shifting a phase of the amplitude modulated excitation signal by the virtual flaw parameter signals, and summing the amplitude modulated and phase shifted excitation signal with the test probe output signal for generating a virtual flaw response signal by the virtual flaw injection circuit. The step for modulating an amplitude may comprise modulating an amplitude of the excitation signal by virtual flaw gain parameter signals and the step for shifting a phase may comprise shifting the phase of the excitation signal by virtual flaw phase shift parameter signals. The step for modulating the amplitude of the excitation signal may comprise the steps for connecting the excitation signal to the input of a variable gain amplifier, controlling the gain of the variable gain amplifier by the virtual flaw gain parameter signal, and providing an amplitude modulated excitation signal at the output of the variable gain amplifier. The step for shifting the phase of the amplitude modulated excitation signal may comprise the steps for connecting the amplitude modulated excitation signal to the input of a variable phase shifter, controlling the phase shift of the variable phase shifter by the virtual flaw phase shift parameter signal, and providing an amplitude modulated and phase shifted excitation signal at the output of the variable phase shifter. The may further comprise the step for basing the nondestructive test system on eddy current technology.
Another embodiment of the present invention is a method for injecting virtual flaw signals into a nondestructive test system, comprising the steps for connecting a flaw signal injection circuit between a nondestructive test instrument and a nondestructive test probe, receiving an excitation signal, a test probe output signal and virtual flaw parameter signals by the flaw signal injection circuit while moving a test probe over a test piece by an inspector, modulating an amplitude and shifting a phase of the excitation signal under control of the virtual flaw parameter signals in the flaw signal injection circuit, summing the amplitude modulated and phase shifted excitation signal with the test probe output signal for generating a virtual flaw response signal by the virtual flaw injection circuit, and sending the virtual flaw response signal from the virtual flaw injection circuit to a test probe input of the nondestructive test instrument for display of virtual and actual flaws to an inspector. The step for receiving virtual flaw parameter signals may further comprise receiving virtual flaw parameters signals determined by the steps for reading test probe position signals for indicating test probe positions relative to a test piece, reading test probe liftoff measurement signals for indicating test probe liftoff from the test piece, reading a virtual flaw map for the test piece stored in a memory for determining uncorrected virtual flaw parameter signals based on the test probe position signals, and applying liftoff correction based on the test probe liftoff measurement signals to the uncorrected virtual flaw parameter signals for determining corrected virtual flaw parameter signals. The step for modulating an amplitude may comprise modulating an amplitude of the excitation signal by virtual flaw gain parameter signals and the step for shifting a phase may comprise shifting the phase of the excitation signal by virtual flaw phase shift parameter signals. The step for modulating the amplitude of the excitation signal may comprise the steps for connecting the excitation signal to the input of a variable gain amplifier, controlling the gain of the variable gain amplifier by the virtual flaw gain parameter signal, and providing an amplitude modulated excitation signal at the output of the variable gain amplifier. The step for modulating the amplitude of the excitation signal may comprise the steps for connecting the excitation signal to a high terminal of an input digital potentiometer, connecting a wiper terminal of the input digital potentiometer to a noninverting input of a differential amplifier, connecting a wiper terminal of a feedback digital potentiometer to an inverting input of the differential amplifier, connecting an output of the differential amplifier to a high terminal of the feedback digital potentiometer, connecting a low terminal of the input digital potentiometer and the feedback digital potentiometer to ground reference potential, connecting the virtual flaw gain parameter signal to a control input of the input digital potentiometer and a control input of the feedback digital potentiometer, and providing an amplitude modulated excitation signal at the output of the differential amplifier. The step for shifting the phase of the amplitude modulated excitation signal may comprise the steps for connecting the amplitude modulated excitation signal to the input of a variable phase shifter, controlling the phase shift of the variable phase shifter by the virtual flaw phase shift parameter signal, and providing an amplitude modulated and phase shifted excitation signal at the output of the variable phase shifter. The step for shifting the phase of the amplitude modulated excitation signal may comprise the steps for connecting three identical phase shift circuits in a cascade configuration, including the steps for connecting an input of a first phase shift circuit to the amplitude modulated excitation signal, connecting an output of the first phase shift circuit to an input of a second phase shift circuit, connecting an output of the second phase shift circuit to an input of a third phase shift circuit, providing an output of the third phase shift circuit as the amplitude modulated and phase shifted excitation signal, and shifting the phase of a signal at an input of each phase shift circuit, including the steps for connecting the input signal of each phase shift circuit to a first terminal of an input resistor and a first terminal of an input capacitor, connecting a second terminal of the input capacitor to a noninverting input of a differential amplifier and a high terminal of a digital potentiometer, connecting a wiper terminal and a low terminal of the digital potentiometer to a ground reference potential, connecting a second terminal of the input resistor to a first terminal of a feedback resistor and an inverting input of the differential amplifier, connecting a second terminal of the feedback resistor to an output of the differential amplifier, the output of the differential amplifier providing an output of the phase shift circuit, and connecting the virtual flaw phase shift parameter signal to a control input of the input digital potentiometer for varying a phase shift of the phase shift circuit. The step for shifting the phase of a signal at an input of each phase shift circuit may comprise shifting of the input signal between 0 and 120 degrees as represented by the phase shift circuit output signal. The method may further comprise the step for deriving the virtual flaw map from the group consisting of a model and premeasured flaws. The nondestructive test instrument and a nondestructive test probe may be based on eddy current technology. The method may further comprise selecting a test probe from the group consisting of a single element probe, a dual element probe and a triple element probe.
Yet another embodiment of the present invention is a system for injecting virtual flaw signals into a nondestructive test system, comprising means for moving a test probe over a test piece by an inspector, means for providing an excitation signal from the nondestructive test system to the test probe and a virtual flaw injection circuit, means for determining virtual flaw parameter signals from test probe position signals and a stored virtual flaw map for the test piece, means for sending the virtual flaw parameter signals and an output signal from the test probe to the virtual flaw injection circuit, means for processing the excitation signal and the test probe output signal using the virtual flaw parameter signals for generating a virtual flaw response signal by the virtual flaw injection circuit, means for transmitting the virtual flaw response signal to a test probe input of the nondestructive test system, and means for displaying actual and virtual flaws to the inspector from the nondestructive test system. The means for determining virtual flaw parameter signals may further comprise means for reading test probe position signals for indicating test probe positions relative to a test piece, means for reading test probe liftoff measurement signals for indicating test probe liftoff from the test piece, means for reading a virtual flaw map for the test piece stored in a memory for determining uncorrected virtual flaw parameter signals based on the test probe position signals, and means for applying a liftoff correction based on the test probe liftoff measurement signals to the uncorrected virtual flaw parameter signals for determining corrected virtual flaw parameter signals. The means for processing may further comprise means for modulating an amplitude of the excitation signal by the virtual flaw parameter signals, means for shifting a phase of the amplitude modulated excitation signal by the virtual flaw parameter signals, and means for summing the amplitude modulated and phase shifted excitation signal with the test probe output signal for generating a virtual flaw response signal by the virtual flaw injection circuit. The means for modulating an amplitude may comprise means for modulating an amplitude of the excitation signal by virtual flaw gain parameter signals and the means for shifting a phase may comprise means for shifting the phase of the excitation signal by virtual flaw phase shift parameter signals. The means for modulating the amplitude of the excitation signal may comprise means for connecting the excitation signal to the input of a variable gain amplifier, means for controlling the gain of the variable gain amplifier by the virtual flaw gain parameter signal, and means for providing an amplitude modulated excitation signal at the output of the variable gain amplifier. The means for shifting the phase of the amplitude modulated excitation signal may comprise the steps for the amplitude modulated excitation signal connected to the input of a variable phase shifter, the phase shift of the variable phase shifter controlled by the virtual flaw phase shift parameter signal, and an amplitude modulated and phase shifted excitation signal provided at the output of the variable phase shifter. The system may further comprise the nondestructive test system based on eddy current technology.
A further embodiment of the present invention includes a system for injecting virtual flaw signals into a nondestructive test system, comprising a flaw signal injection circuit connected between a nondestructive test instrument and a nondestructive test probe, an excitation signal, a test probe output signal and virtual flaw parameter signals received by the flaw signal injection circuit while moving a test probe over a test piece by an operator, an amplitude and a phase shift of the excitation signal being controlled by the virtual flaw parameter signals in the flaw signal injection circuit, the amplitude modulated and phase shifted excitation signal being summed with the test probe output signal for generating a virtual flaw response signal by the virtual flaw injection circuit, and the virtual flaw response signal being sent from the virtual flaw injection circuit to a test probe input of the nondestructive test instrument for display of virtual and actual flaws to an inspector. The virtual flaw parameter signals may further comprise virtual flaw parameters signals determined by test probe position signals for indicating test probe positions relative to a test piece, test probe liftoff measurement signals for indicating test probe liftoff from the test piece, a virtual flaw map for the test piece stored in a memory for determining uncorrected virtual flaw parameter signals based on the test probe position signals, and liftoff correction based on the test probe liftoff measurement signals to the uncorrected virtual flaw parameter signals for determining corrected virtual flaw parameter signals. The means for modulating an amplitude may comprise means for modulating an amplitude of the excitation signal by virtual flaw gain parameter signals and the means for shifting a phase may comprise means for shifting the phase of the excitation signal by virtual flaw phase shift parameter signals. The means for modulating the amplitude of the excitation signal may comprise means for connecting the excitation signal to the input of a variable gain amplifier, means for controlling the gain of the variable gain amplifier by the virtual flaw gain parameter signal, and means for providing an amplitude modulated excitation signal at the output of the variable gain amplifier. The means for modulating the amplitude of the excitation signal may comprise the excitation signal connected to a high terminal of an input digital potentiometer, a wiper terminal of the input digital potentiometer connected to a noninverting input of a differential amplifier, a wiper terminal of a feedback digital potentiometer connected to an inverting input of the differential amplifier, an output of the differential amplifier connected to a high terminal of the feedback digital potentiometer, a low terminal of the input digital potentiometer and the feedback digital potentiometer connected to ground reference potential, the virtual flaw gain parameter signal connected to a control input of the input digital potentiometer and a control input of the feedback digital potentiometer, and an amplitude modulated excitation signal provided at the output of the differential amplifier. The means for shifting the phase of the amplitude modulated excitation signal may comprise the steps for the amplitude modulated excitation signal connected to the input of a variable phase shifter, the phase shift of the variable phase shifter controlled by the virtual flaw phase shift parameter signal, and an amplitude modulated and phase shifted excitation signal provided at the output of the variable phase shifter. The means for shifting the phase of the amplitude modulated excitation signal may comprise three identical phase shift circuits connected in a cascade configuration, including an input of a first phase shift circuit connected to the amplitude modulated excitation signal, an output of the first phase shift circuit connected to an input of a second phase shift circuit, an output of the second phase shift circuit connected to an input of a third phase shift circuit, an output of the third phase shift circuit provided as the amplitude modulated and phase shifted excitation signal, and each phase shift circuit including the input signal of each phase shift circuit connected to a first terminal of an input resistor and a first terminal of an input capacitor, a second terminal of the input capacitor connected to a noninverting input of a differential amplifier and a high terminal of a digital potentiometer, a wiper terminal and a low terminal of the digital potentiometer connected to a ground reference potential, a second terminal of the input resistor connected to a first terminal of a feedback resistor and an inverting input of the differential amplifier, a second terminal of the feedback resistor connected to an output of the differential amplifier, the output of the differential amplifier providing an output of the phase shift circuit, and the virtual flaw phase shift parameter signal connected to a control input of the input digital potentiometer for varying a phase shift of the phase shift circuit. The system wherein each phase shift circuit may shift the input signal between 0 and 120 degrees as represented by the phase shift circuit output signal. The system may further comprise the virtual flaw map derived from the group consisting of a model and premeasured flaws. The nondestructive test instrument and a nondestructive test probe may be based on eddy current technology. The system may further comprise a test probe selected from the group consisting of a single element probe, a dual element probe and a triple element probe.